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…#5889)

Fixes flutter/flutter#19571

Fixes flutter/flutter#19566

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These scripts generate the image we used to test flutter/engine in Cirrus.

This reduces the build time from 5 minutes to 3 minutes as we no longer need to cold start a GCE instance. Moreover, we can now compile the host engine using this container.

Using a custom container image, we reduce the test time from 5 minutes to 2 minutes as we no longer run gclient sync from zero.

In the future, we may be able to cache the ninja output in the image (which probably gets updated daily) so we no longer compile from zero.

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Don't emit a "VSYNC" event when running on Fuchsia, as traces on Fuchsia
are typically recorded across the whole system, causing the events to
collide with each other.

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…#18886) (#5858)

* Deprecate -[FlutterDartProject initFromDefaultSourceForConfiguration] (#18886)

`-[FlutterDartProject initFromDefaultSourceForConfiguration]` no
longer seems very useful.  It calls `-initWithPrecompiledDartBundle:`
or `-initWithFlutterAssets:dartMain:packages:`, but since it now
passes `nil` for all arguments, both paths end up doing the same
thing.

Additionally, `-initFromDefaultSourceForConfiguration` is awkward to
use in Swift.  The automatically generated Swift interface is:

    public convenience init!(fromDefaultSourceForConfiguration: ())

and it's not obvious how to call that.

Let's deprecate `-initFromDefaultSourceForConfiguration` and instead
expect callers to use the existing `-init` method. (We can make
`-init` do different things for different build configurations later
if necessary.)

Bonus: Rename some parameters to make it more obvious when they may
be `nil`.